NEC Article 409

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NEC Article 409 UL508A Industrial Control
Panels

• Troy Miesse/ IE Business Development

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Industrial Control Panels
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Agenda

• NFPA 70 National Electric Code (NEC)
• Short Circuit Current Ratings
• Article 409 Industrial Control Panels
• UL508A (Supplement SB)
• Arc Flash and NFPA 70E
• Personnel Protection Equipment

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National Electric Code

• NFPA 70 National Electric Code (NEC)
• Most states and Authorities Having Jurisdiction
  (AHJ) have adopted the 2005 NEC.
• NEC is updated approximately every 3 years
• Article 409 Industrial Control Panels was added
  to the NEC in 2005
• Article 409 requires all industrial control
  panels to be marked with an SCCR.
• Empty enclosures do not have a SCCR

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What is a SCCR ?

• A Short Circuit Current Rating is the maximum
  current a device or panel can safely withstand
  for 3 AC electrical cycles (50 msec.) or while an
  over-current protective device operates.
• SCCR is usually expressed in RMS kA at the system
  voltage. Example 18 kA at 480 VAC
• RMS is the Root Mean Squared AC current.
• The SCCR of a fuse or circuit breaker is the same
  as its Interrupting Rating (IR).

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NEC Article 409

• Industrial Control Panel - An assembly of two or
  more components such as motor controllers,
  relays, CBs, etc..and related control devices
• Industrial Control Panels do not include the
  controlled equipment.
• Requires all industrial control panels to be
  marked with SCCR This is a major addition!
• This addition will impact control panel builders,
  OEMs and end users in numerous ways
• - How control panel are designed and marked
• - The selection of power circuit components.
• - The specification of preferred manufacturers.
• - How control panels are installed and modified.

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Before the NEC 2005

• Only Industrial Machinery required marking for
  interrupting rating or SCCR of main over-current
  protective device
• Industrial control panels, HVAC control panels,
  motor controllers, and meter disconnects were not
  required to be marked with SCCR

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2005 NEC

• The 2005 NEC requires SCCR markings on all
• Industrial Control Panels -NEC Article 409
• Motor controllers -NEC Article 430.8
• HVAC controllers -NEC Article 440.4(B)
• Industrial machinery -NEC Article 670.3
• Meter disconnects -NEC Article 230.82(3)

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How do I Determine the Panel SCCR ? NEC Article
409.110 states that the SCCR of an industrial
control panel is based on one of the following

• SCCR of a Listed and labeled assembly
• SCCR based on the use of an approved method
• UL 508A Supplement SB is given as an example of
  an approved method
• Method approved by local electrical inspector
  (AHJ)
• Engineer (PE) approved apparent RMS method.

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How do I Determine the Panel SCCR ? NEC Article
409.110 states that the SCCR of an industrial
control panel is based on one of the following

• SCCR of a Listed and labeled assembly
• Easy enough if you just buying the control panel
• Not an option if you are building or specifying
  a control panel

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How do I Determine the Panel SCCR ? NEC Article
409.110 states that the SCCR of an industrial
control panel is based on one of the following

• SCCR of a Listed and labeled assembly
• SCCR based on the use of an approved method
• UL 508A Supplement SB is given as an example of
  an approved method

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UL 508A Standard

• UL 508A standard is Industrial Control Panels
• The standard covers industrial control panels
  intended for general industrial use, operating at
  a voltage of 600 volts or less
• This equipment is intended for installation in
  ordinary locations, in accordance with the
  National Electrical Code, ANSI/NFPA 70
• Supplement SB is included to help determine SCCR
  for Industrial Control panels by providing, among
  other things, default SCCR ratings for common
  components

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UL 508A Supplement SB

• UL 508A Supplement SB describes three steps to
• determine the SCCR of industrial control panels
• Determine the SCCR of all individual power
  components by one of the following methods
• - SCCR rating marked on the component
• - Use assumed SCCRs in table SB 4.1 of Supplement
  SB
• - Use the tested SCCR from component combinations
  per UL508
• Modify the SCCR of certain series combinations if
  current-limiting devices are used in the feeder
  circuit.
• Determine the overall panel SCCR according to
  charts in SB4.4
• - Flow chart that help understanding and
  assignment of SCCR

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UL 508A Standard Supplement SB
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UL 508A Supplement SB (review)

• UL 508A Supplement SB describes three steps to
• determine the SCCR of industrial control panels
• Determine the SCCR of all individual power
  components by one of the following methods
• - SCCR rating marked on the component
• - Use assumed SCCRs in table SB 4.1 of Supplement
  SB
• - Use the tested SCCR from component combinations
  per UL508
• Modify the SCCR of certain series combinations if
  current-limiting devices are used in the feeder
  circuit.
• Determine the overall panel SCCR according to
  charts in SB4.4
• - Flow chart that help understanding and
  assignment of SCCR

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UL 508A Supplement SB4.4 Chart
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SCCR Calculation Example Individual SCCRs
Main CB
Control Trans W/ fuses

• Power Circuit SCCR at 480V
• Main CB 30kA
• Contactor 5kA
• Overload Relay 5kA
• Fuses on C-Trans 200kA
• Control Circuit
• Control Trans ---
• Control Relay ---
• Terminal Blocks ---

Control Relay
Terminal Blocks
Contactor W/ Overload
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SCCR Calculation Example Individual SCCRs
Main CB
Control Trans W/ fuses

• Power Circuit SCCR at 480V
• Main CB 30kA
• Contactor 5kA
• Overload Relay 5kA
• Fuses on C-Trans 200kA
• If no additional information is available the the
  Industrial Control Panel must be rated at the
  lowest rating of any component 5kA

Control Relay
Terminal Blocks
Contactor W/ Overload
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SCCR Calculation Example Tested Combinations
Main CB
Control Trans W/ fuses

• Power Circuit SCCR at 480V
• Main CB 30kA
• Contactor 5kA
• Overload Relay 5kA
• Fuses on C-Trans 200kA
• Control Circuit
• Control Trans ---
• Control Relay ---
• Terminal Blocks ---

Control Relay
Terminal Blocks
Contactor W/ Overload
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SCCR Calculation Example Tested Combinations

• Power Circuit SCCR at 480V
• Main CB
• Contactor 30kA
• Overload Relay
• Fuses on C-Trans 200kA
• UL508 component combination test results show
  that the CB and starter combination can be rated
  at 30kA. The Industrial Control Panel can now be
  rated at a higher SCCR 30kA

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How to Increase SCCR

• Use components and approved combinations with
  higher rated SCCRs.
• Use current limiting over-current protective
  devices (CB/ fuses) whenever possible.
• Replace low interrupting rated over-current
  protection with higher rated ones (retrofit).
• According to UL 508A Articles SB3.2 and SB4.4,
  the SCCR of the panel cannot be greater than the
  interrupting rating of any over-current
  protective device in branch circuits or in the
  primary of control circuits.

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Industrial Control Panel Marking

• Per NEC an industrial control panel shall be
  marked with the
• following information that is plainly visible
  after installation
• Manufacturers name, trademark, etc.
• Supply voltage, phase, frequency and full-load
  current
• SCCR
• Identify as service equipment (if applicable)
• Electrical wiring diagram or the index number
• Enclosure type (rating) number

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Panel Marking
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On-site Compliance

• On-site engineer provides the following
  information
• Available short circuit current at installation
  point
• Planned SCCR of the equipment or panel
• Inspector compares actual marked SCCR to the
  provided data
• If SCCR data is accurate then approval is give
• Inaccurate or incomplete data can result in
  red-tag and may require additional analysis
• Engineers and inspectors must work together

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Industrial Control Panel Marking

• Why are Marked SCCRs Important?
• Needed to ensure compliance with NEC and UL508A
• Helps to eliminate hazards where components and
  equipment could be applied above their ratings
• Simplifies inspection approval process for
  engineers and inspectors
• New installations
• Machinery relocation
• Contributes to a safe electrical system
• Guards against arc-flash hazards

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What is Arc Flash?
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What is an Arc-Flash?

• A flow of current through the air between phase
  conductors or phase conductors and neutral or
  ground
• Usually unintentional
• Causes include
• Human error
• Insulation failure
• Animal interference
• 5-10 times per day in U.S. - arc flash accidents
  injure or kill a worker

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Arc-Flash Hazard Standards

• OSHA Standards 29-CFR, Part 1910 Work safety
• NFPA 70 (NEC) Warning label requirements
• NFPA 70E 2004 Appropriate work practices
• IEEE 1584 2002 Arc flash hazard calculations

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Arc-Flash Hazard

• An arc flash hazard is defined in NFPA 70E as a
  dangerous condition associated with the release
  of energy caused by an electric arc
• The NEC requires a label that states the
  existence of an arc flash hazard
• OSHA regulations state the employers shall
  protect employees from recognized hazards
• NFPA 70E tells employers how to protect employees
  from recognized hazards
• IEEE 1584 shows the math to calculate the hazards

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Arc-Flash Panel Marking

• Flash Protection Boundary 2.9 ft
• Boundary where person could receive 2nd
  degree burns from arc flash - 1.2 cal/cm2

• Incident Energy 2.3 Cal/ cm2
• Amount of energy produced during an arc flash

• Working Distance 18 in.
• The distance between worker and arc source

• Required PPE Level 1
• Protective clothing and apparatus to protect
  against arc flash injury

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Arc-Flash Panel Marking

• Shock Hazard Voltage 3450 VAC
• Potential voltage levels that can be delivered

• Limited Approach 10.0 ft.
• Shock protection boundary Qualified personnel
  only unless escorted

• Restricted Approach 2.2 ft.
• Shock protection boundary Qualified personnel
  only with PPE

• Prohibited Approach 0.6 ft.
• Shock protection boundary Qualified personnel
  only with PPE (contact is possible)

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Arc-Flash Hazard

• Arc Flash Hazard boundaries are based on voltage,
  available short-circuit current and predicted
  fault duration
• Different levels mean different protective gear
  required when servicing a panel ( i.e opening the
  panel door)
• This applies to all personnel that may need to
  access the panel or be exposed to live equipment
• May need an Arc Flash analysis performed
• Determine arc flash protection boundaries
• Personnel Protection Equipment (PPE) and training
  is a must

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What Does OHSA Say?

• OSHA regulations state in 1910.333 (a) that
  workers should not work on or near exposed live
  equipment (greater than 50 volts) except for one
  of two reasons
• De-energizing introduces additional or increased
  hazards such as cutting ventilation to a
  hazardous location.
• Infeasible due to equipment design or operational
  limitations such as when voltage testing is
  required for diagnostics. When it is necessary to
  work on energized equipment you should follow
  safe work practices including assessing the
  risks, wearing proper PPE, and using the proper
  tools

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Personnel Protection Equipment - PPE

• PPE is designed to minimize injuries
• NFPA 70E requires any body part that is within
  the flash protection boundary be protected by
  using appropriate PPE (OSHA say basically the
  same thing)
• Hard hat
• Safety glasses or goggles (Arc-rated face shield)
• Hearing protection
• Gloves (leather, rubber)
• Flash suit (multi-layer clothes)
• Leather work shoes

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Personnel Protection Equipment - PPE

• Notes
• 1 cal/ cm2 equates to holding ones finger over
  the tip of a flame of a cigarette lighter for 1
  sec.
• 1.2 cal/ cm2 is considered the threshold for a
  curable burn (second-degree)

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PPE Protection From Arc-Flash!
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How to Avoid Arc-Flash Hazards

• Build control panels within the properly rated
  enclosures
• Minimize exposure to energized equipment
• Follow proper lockout/ tag-out procedures
• Design into control cabinets access options that
  will allow programming, data acquisition and
  system adjustment without having to open the
  panel door
• Maintain and update equipment and documentation
• Conduct safety training for all personnel

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Industrial Control Panel Access Options

• Properly applied they can reduce arc-flash
  hazards
• Save time and money - No PPE required
• Maintains enclosure type ratings
• Many options available
• RJ 45, SUB-D9, USB, etc.
• Eternal shelves
• Document enclosures
• Operator panels
• Viewing windows

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Updated Industrial Control Panel
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Industrial Control Panels
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NEC Article 409 UL508A Industrial Control
Panels

• Troy Miesse/ IE Business Development